/*
 * HashCodeUtil.java
 *
 */

package org.lpp.util;

import java.lang.reflect.Array;

/**
 * Collected methods which allow easy implementation of <code>hashCode</code>.
 *
 * Example use case:
 * <pre>
 *  public int hashCode(){
 *    int result = HashCodeUtil.SEED;
 *    //collect the contributions of various fields
 *    result = HashCodeUtil.hash(result, fPrimitive);
 *    result = HashCodeUtil.hash(result, fObject);
 *    result = HashCodeUtil.hash(result, fArray);
 *    return result;
 *  }
 * </pre>
 *
 * @author rhisld
 */
public class HashCodeUtil {
    private static final int fODD_PRIME_NUMBER = 37;
    
    /**
     * An initial value for a <code>hashCode</code>, to which is added contributions
     * from fields. Using a non-zero value decreases collisons of <code>hashCode</code>
     * values.
     */
    public static final int SEED = 23;
    
    /**
     * booleans.
     */
    public static int hash( int aSeed, boolean aBoolean ) {
        System.out.println("boolean...");
        return firstTerm( aSeed ) + ( aBoolean ? 1 : 0 );
    }
    
    /**
     * chars.
     */
    public static int hash( int aSeed, char aChar ) {
        System.out.println("char...");
        return firstTerm( aSeed ) + (int)aChar;
    }
    
    /**
     * ints.
     * Implementation Note
     * Note that byte and short are handled by this method, through
     * implicit conversion.
     */
    public static int hash( int aSeed , int aInt ) {
        System.out.println("int...");
        return firstTerm( aSeed ) + aInt;
    }
    
    /**
     * longs.
     */
    public static int hash( int aSeed , long aLong ) {
        System.out.println("long...");
        return firstTerm(aSeed)  + (int)( aLong ^ (aLong >>> 32) );
    }
    
    /**
     * floats.
     */
    public static int hash( int aSeed , float aFloat ) {
        return hash( aSeed, Float.floatToIntBits(aFloat) );
    }
    
    /**
     * doubles.
     */
    public static int hash( int aSeed , double aDouble ) {
        return hash( aSeed, Double.doubleToLongBits(aDouble) );
    }
    
    /**
     * <code>aObject</code> is a possibly-null object field, and possibly an array.
     *
     * If <code>aObject</code> is an array, then each element may be a primitive
     * or a possibly-null object.
     */
    public static int hash( int aSeed , Object aObject ) {
        int result = aSeed;
        if ( aObject == null) {
            result = hash(result, 0);
        } else if ( ! isArray(aObject) ) {
            result = hash(result, aObject.hashCode());
        } else {
            int length = Array.getLength(aObject);
            for ( int idx = 0; idx < length; ++idx ) {
                Object item = Array.get(aObject, idx);
                //recursive call!
                result = hash(result, item);
            }
        }
        return result;
    }
    
    private static int firstTerm( int aSeed ){
        return fODD_PRIME_NUMBER * aSeed;
    }
    
    private static boolean isArray(Object aObject){
        return aObject.getClass().isArray();
    }
}